Brake failure explanation

Hello everyone,

Last summer, the brakes on my 1998 Subaru Legacy failed while driving down a steep mountain (thankfully my partner and I survived mostly uninjured). I tried everything I could think of to slow down, but it was a 12% grade hill and we were picking up too much speed for anything to be effective. After about two minutes of driving 70mph down the hill, we reached a flat surface and I intentionally crashed my car into the side of the mountain and a ditch to stop us.

Although I obviously don’t drive this car anymore, I’m curious as to why this happened and if anyone has ideas about an explanation. I had this car serviced often, and had taken it in shortly before the crash. The mechanics paid attention to the brakes specifically and found that the brake fluid was in a good state, my brake pads were working, etc. They said I had no issues and the car was safe and had at least 50,000 miles left on it (at the time it had about 198,000).

Prior to the brake failure, I had observed no issues whatsoever with the brake system. The brake light was not on, there were no squealing or grinding noises, no scraping, no leaking fluid, no burning smell while driving, and the brake pedal was not soft or spongy.

Just before the brakes failed, I had been driving on a gravel mountain road. It was pretty well-used and maintained, but there were a few bumps along the way. The brakes failed about two minutes after I had left the gravel road and returned to the paved hill. This is the only event that was out of the ordinary, and I wonder if that rocky terrain affected the brake system.

No mechanic has been able to give me an answer as to why this occurred and have called it a “freak accident.” While my current car works well, this was a very traumatic experience and I want to do anything I can to prevent it from happening again, as well as be aware of signs I could have missed that indicate brake problems. Thank you for your help!

If you drive down a steep mountain and only use the brakes to slow down, it can cause brake fade.



What actually did you feel? A hard pedal that was not slowing the car? That would be brake fade.

Or a very long travel pedal that did not slow the car? That would be boiling the brake fluid.

Both can be prevented by shifting to a lower gear to slow the car and not using so much brake.


Thanks for your comment! It was a very long travel pedal; when I put my foot on the brake, it went all the way to the floor and did not slow it down whatsoever. There was no give.

As for the gears, I was driving in third gear when they failed. I shifted it into second and pulled the emergency brake. This slowed it down for about five seconds, but we started picking up speed again (especially after making a sharp turn around corners).

Thanks! I will look into this.

Sounds like old brake fluid that was overheating. It’s highly recommended that brake fluid be changed ever so often to prevent problems like this.There are much better alternatives to stopping rather than intentional crashes.

Yanking the park brake along with downshifting the transmission are a couple of methods along with a last ditch resort of shifting the transmission into the PARK position (Assuming an automatic trans)

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Thank you, I appreciate your insight about the brake fluid! That is a good point and could likely have contributed/caused it. I also agree that intentional crashes are usually a pretty bad choice. However, in this situation intentionally crashing the car was the only way to prevent us from crashing head-on into houses or spinning out into a busy freeway (police officers and tow truck guy told us this).

I agree with others that your brake fluid boiled. I drove in CA a few years ago and drove down a few extremely steep mountain roads (I think one was around 20% grade). I used first gear, not second, as it was the only gear that would keep our speed down without constant brake usage. I dabbed my brakes occasionally and the use of first gear kept the brakes cool and useful. Every time I shifted into second gear the vehicle took off so I deemed that gear not to be useful on the mountain road I was descending.


Could be that the master cylinder went bad if there is no apparent leak anywhere. If the fluid is leaking past the seals inside the cylinder, the pedal may feel firm for a moment but won’t hold steady; it’ll feel spongy and keep sinking towards the floor. When a master cylinder begins to fail, sometimes the brakes will feel fine one second and lose braking power the next giving you this effect.

Hi Kendall:
I agree with the others that it sounds like your brake fluid was boiling.

Two questions:

  1. Prior to your experiencing the brake failure on that ride down the mountain, did you happen to be using or riding your brakes a lot to control your speed?

  2. The car is 23 years old. Do you remember when the brake fluid was last changed? I ask because brake fluid tends to absorb moisture over time. As it does, the boiling point of the brake fluid is reduced, which makes it more prone to boiling under heavy brake usage.

As Corollaguy noted, if you do experience any of the low or no pedal symptoms during normal driving, then do consider the master cylinder. So far in what you wrote, it doesn’t seem like that, but do note it.

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This is exactly what I was thinking. Brake fluid is hygroscopic (absorbs water). Over time if it absorbs too much water then under braking conditions the fluid heats up and this can boil the water and drastically compromise the braking system.

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Why not first?

An additional issue on top of the brake fluid boiling is the liklihood that this brake system is diagonally split. In the late 60s brake systems were changed to a dual system so if a leak occured anywhere in the system, only half would leak out and the other half could be used to stop the car. Rear drive cars split that system front/rear. When front wheel drive cars came about, they were split diagonally because the rear brakes don’t do much and would not slow the car effectively if the front leaked out.

The net effect of that sine the front brakes are more likely to boil the fluid; when they do, you lose everything. In the front/rear split, boiled front brake fluid still allows the rears to work.


Since this is an event that’s rarely reported, it’s more likely that it comes from a mixture of unfortunate events - some of them have been explained here. Did a mechanic ever look over the car after the crash?

And, sideswiping the side of a hill deliberately seems like a reasonable choice under these extreme conditions.


It might have been an internal leak in the master cylinder. Pumping the brake pedal might have been enough to produce more fluid pressure, at least for a while. Do you remember if you tried that?

Reminds me a of a car I bought, cheap, from a college friend. “The brakes work, you just have to pump 'em.” A new master cylinder was my first repair on that one.


sorry that happened to you. something to keep in mind, using the cheapest set of brake pads might be ok for around town but might not be ok for other conditions. Im not saying you did that, just thought I would mention it. like they say you get what you pay for.

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I remember that it was Tom and Ray who first told me about the fluid boiling problem. It might even have been the answer to a puzzler. One choice I haven’t seen in the answers yet is that this can also occur if a brake is dragging at one wheel. I just had that problem with a frozen caliper, which I diagnosed by a warm wheel after a short drive (warmer than the opposite side). I did not drive enough to boil fluid.

In that case it would happen cruising on flat ground.
I think this would not have happened if the OP had changed brake fluid every 3 years.

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Did this happen on the first application of the brake? Or after using the brake for a period of time to control the vehicle’s speed on the descent?

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Possible failure of the linkage between the pedal and the master cylinder. A pin with a retainer. If the retainer is missing or falls off, The pin will eventually work its way out. Almost happened to me once. Cotter pin was missing and the pin was about to fall out.